Improved two-temperature model of hypersonic thermochemical nonequilibrium flows with correction of non-Boltzmann effect for air

The accurate determination of chemical reaction rates is a prerequisite for precisely simulating hypersonic thermochemical nonequilibrium flows. Traditional two-temperature (2-T) models fail to capture the non-Boltzmann (NB) effects of vibrational energy-level distributions. This deficiency leads to inaccurate prediction of chemical reaction rates and hinders precise simulation of nonequilibrium flow. This paper conducted computational studies on the oxygen dissociation and recombination reactions, which are most significantly influencing nonequilibrium relaxation in air components, using the high-fidelity state-to-state (STS) method. The effects and patterns of NB effects on these reactions were investigated, and a correction method incorporating NB effects was proposed. This method was further integrated with the single-group linear maximum entropy model considering internal energy nonequilibrium, resulting in an improved thermochemical nonequilibrium model that accounts for NB effects. The proposed improved model provides accurate chemical reaction rate values. Numerical simulations of relaxation processes behind normal shock waves and flow fields around a hemisphere were performed using this model, yielding results consistent with STS method calculations. The computed outcomes exhibited better agreement with experimental data compared to traditional 2-T Park model, demonstrating the feasibility and validity of the proposed improved air-component thermochemical nonequilibrium model.